The disclosure of Japanese Patent Application No. HEI 10-197754 filed on Jul. 13, 1998, including the specification, drawings and abstract, is incorporated herein by reference in its entirety.
1. Field of the Invention
The present invention relates to a lamination molding resin-coated sand suited for lamination molding and a lamination molding method using the lamination molding resin-coated sand.
2. Description of the Related Art
In recent years, the development of the lamination molding technique (as disclosed by, for example, U.S. Pat. No. 4,247,508) is underway. With this lamination molding technique, a sand application step of applying resin-coated sand and forming a sand layer and a laser radiation step of radiating a laser beam to the sand layer to thereby form a solidified layer are alternately repeated, thereby sequentially forming many solidified layers and eventually forming a two-dimensional article.
The resin-coated sand, which has been conventionally provided by means of this lamination molding technique, is obtained by coating sand particles with resin and used for molding a shell casting mold by means of the shell molding method. Therefore, with the lamination molding technique using the above resin-coated sand, the enhancement of accuracy for the shape and dimensions of a formed article is limited. In the shell molding method, the cavity of a heated mold is filled with resin-coated sand, thereby thermally curing the resin of the resin-coated sand which contact with the cavity molding surface of the mold and forming a shell casting mold.
Namely, the sand particles of the resin-coated sand as conventionally provided have relatively large diameters, i.e., about 200 to 300 xcexcm so as to ensure the discharge efficiency of discharging gas generated from the shell casting mold. Due to this, as shown in FIG. 7, a sand layer formed by the lamination molding technique, is thin and part of sand particles 53xc3x97 quite likely protrude from the surface of the sand layer 500. If so, the irregularity of the surface of the sand layer 500 tends to increase. Besides, a cured layer, into which part of the sand layer 500 is formed, tends to have an irregular surface. For these reasons, there is a limit to the enhancement of accuracy for the shape and dimensions of a formed article. Further, the shell molding method is intended to thermally cure the resin soon after the resin-coated sand contacts with the high temperature cavity molding surface of the mold. The fusion temperature of the resin is, therefore, as low as 70 to 80xc2x0 C.
With the above-stated resin-coated sand, the enhancement of accuracy for the shape of an article formed by lamination molding has its limit. So does the enhancement of the quality of the formed article have its limit.
The present invention has been made under these circumstances. It is, therefore, an object of the present invention to provide a lamination molding resin-coated sand and a lamination molding method capable of advantageously enhancing the accuracy and quality of a formed article.
A lamination molding resin-coated sand according to the present invention is a lamination molding resin-coated sand used for lamination molding for forming a laminated article by laminating sand layers in thickness direction, and wherein sand particles coated with resin are about 20 to 100 xcexcm in diameter and generally spherical.
A lamination molding method according to the present invention is comprising a step of preparing resin-coated sand of generally spherical sand particles each having a particle diameter of 20 to 100 xcexcm and coated with resin; a sand application step of applying the resin-coated sand to form a thin sand layer; a laser radiation step of radiating a laser beam onto the sand layer to cure the resin; alternately repeating the sand application step and the laser radiation step until sand layers are laminated in thickness direction and an article is formed.
The resin-coated sand of the present invention is advantageous to the enhancement of accuracy for the shape and dimensions of a formed article as well as the quality of the article. The lamination molding method of the present invention is advantageous to the enhancement of accuracy for the shape and dimensions of a formed article as well as of the quality of the article, even if sand layers are thin.